| 1 | /* |
| 2 | * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition. |
| 3 | * |
| 4 | * This program is free software; you can redistribute it and/or modify |
| 5 | * it under the terms of the GNU General Public License as published by |
| 6 | * the Free Software Foundation; either version 2 of the License, or |
| 7 | * (at your option) any later version. |
| 8 | * |
| 9 | * This program is distributed in the hope that it will be useful, |
| 10 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 11 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 12 | * GNU General Public License for more details. |
| 13 | * |
| 14 | * You should have received a copy of the GNU General Public License |
| 15 | * along with this program; if not, write to the Free Software |
| 16 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
| 17 | * |
| 18 | * Copyright IBM Corporation, 2008 |
| 19 | * |
| 20 | * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> |
| 21 | * |
| 22 | * For detailed explanation of Read-Copy Update mechanism see - |
| 23 | * Documentation/RCU |
| 24 | */ |
| 25 | #include <linux/completion.h> |
| 26 | #include <linux/interrupt.h> |
| 27 | #include <linux/notifier.h> |
| 28 | #include <linux/rcupdate.h> |
| 29 | #include <linux/kernel.h> |
| 30 | #include <linux/export.h> |
| 31 | #include <linux/mutex.h> |
| 32 | #include <linux/sched.h> |
| 33 | #include <linux/types.h> |
| 34 | #include <linux/init.h> |
| 35 | #include <linux/time.h> |
| 36 | #include <linux/cpu.h> |
| 37 | #include <linux/prefetch.h> |
| 38 | |
| 39 | #ifdef CONFIG_RCU_TRACE |
| 40 | #include <trace/events/rcu.h> |
| 41 | #endif /* #else #ifdef CONFIG_RCU_TRACE */ |
| 42 | |
| 43 | #include "rcu.h" |
| 44 | |
| 45 | /* Forward declarations for rcutiny_plugin.h. */ |
| 46 | struct rcu_ctrlblk; |
| 47 | static void invoke_rcu_callbacks(void); |
| 48 | static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp); |
| 49 | static void rcu_process_callbacks(struct softirq_action *unused); |
| 50 | static void __call_rcu(struct rcu_head *head, |
| 51 | void (*func)(struct rcu_head *rcu), |
| 52 | struct rcu_ctrlblk *rcp); |
| 53 | |
| 54 | static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; |
| 55 | |
| 56 | #include "rcutiny_plugin.h" |
| 57 | |
| 58 | /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */ |
| 59 | static void rcu_idle_enter_common(long long newval) |
| 60 | { |
| 61 | if (newval) { |
| 62 | RCU_TRACE(trace_rcu_dyntick("--=", |
| 63 | rcu_dynticks_nesting, newval)); |
| 64 | rcu_dynticks_nesting = newval; |
| 65 | return; |
| 66 | } |
| 67 | RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting, newval)); |
| 68 | if (!is_idle_task(current)) { |
| 69 | struct task_struct *idle = idle_task(smp_processor_id()); |
| 70 | |
| 71 | RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task", |
| 72 | rcu_dynticks_nesting, newval)); |
| 73 | ftrace_dump(DUMP_ALL); |
| 74 | WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", |
| 75 | current->pid, current->comm, |
| 76 | idle->pid, idle->comm); /* must be idle task! */ |
| 77 | } |
| 78 | rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */ |
| 79 | barrier(); |
| 80 | rcu_dynticks_nesting = newval; |
| 81 | } |
| 82 | |
| 83 | /* |
| 84 | * Enter idle, which is an extended quiescent state if we have fully |
| 85 | * entered that mode (i.e., if the new value of dynticks_nesting is zero). |
| 86 | */ |
| 87 | void rcu_idle_enter(void) |
| 88 | { |
| 89 | unsigned long flags; |
| 90 | long long newval; |
| 91 | |
| 92 | local_irq_save(flags); |
| 93 | WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0); |
| 94 | if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == |
| 95 | DYNTICK_TASK_NEST_VALUE) |
| 96 | newval = 0; |
| 97 | else |
| 98 | newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE; |
| 99 | rcu_idle_enter_common(newval); |
| 100 | local_irq_restore(flags); |
| 101 | } |
| 102 | EXPORT_SYMBOL_GPL(rcu_idle_enter); |
| 103 | |
| 104 | /* |
| 105 | * Exit an interrupt handler towards idle. |
| 106 | */ |
| 107 | void rcu_irq_exit(void) |
| 108 | { |
| 109 | unsigned long flags; |
| 110 | long long newval; |
| 111 | |
| 112 | local_irq_save(flags); |
| 113 | newval = rcu_dynticks_nesting - 1; |
| 114 | WARN_ON_ONCE(newval < 0); |
| 115 | rcu_idle_enter_common(newval); |
| 116 | local_irq_restore(flags); |
| 117 | } |
| 118 | EXPORT_SYMBOL_GPL(rcu_irq_exit); |
| 119 | |
| 120 | /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */ |
| 121 | static void rcu_idle_exit_common(long long oldval) |
| 122 | { |
| 123 | if (oldval) { |
| 124 | RCU_TRACE(trace_rcu_dyntick("++=", |
| 125 | oldval, rcu_dynticks_nesting)); |
| 126 | return; |
| 127 | } |
| 128 | RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting)); |
| 129 | if (!is_idle_task(current)) { |
| 130 | struct task_struct *idle = idle_task(smp_processor_id()); |
| 131 | |
| 132 | RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task", |
| 133 | oldval, rcu_dynticks_nesting)); |
| 134 | ftrace_dump(DUMP_ALL); |
| 135 | WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", |
| 136 | current->pid, current->comm, |
| 137 | idle->pid, idle->comm); /* must be idle task! */ |
| 138 | } |
| 139 | } |
| 140 | |
| 141 | /* |
| 142 | * Exit idle, so that we are no longer in an extended quiescent state. |
| 143 | */ |
| 144 | void rcu_idle_exit(void) |
| 145 | { |
| 146 | unsigned long flags; |
| 147 | long long oldval; |
| 148 | |
| 149 | local_irq_save(flags); |
| 150 | oldval = rcu_dynticks_nesting; |
| 151 | WARN_ON_ONCE(rcu_dynticks_nesting < 0); |
| 152 | if (rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) |
| 153 | rcu_dynticks_nesting += DYNTICK_TASK_NEST_VALUE; |
| 154 | else |
| 155 | rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; |
| 156 | rcu_idle_exit_common(oldval); |
| 157 | local_irq_restore(flags); |
| 158 | } |
| 159 | EXPORT_SYMBOL_GPL(rcu_idle_exit); |
| 160 | |
| 161 | /* |
| 162 | * Enter an interrupt handler, moving away from idle. |
| 163 | */ |
| 164 | void rcu_irq_enter(void) |
| 165 | { |
| 166 | unsigned long flags; |
| 167 | long long oldval; |
| 168 | |
| 169 | local_irq_save(flags); |
| 170 | oldval = rcu_dynticks_nesting; |
| 171 | rcu_dynticks_nesting++; |
| 172 | WARN_ON_ONCE(rcu_dynticks_nesting == 0); |
| 173 | rcu_idle_exit_common(oldval); |
| 174 | local_irq_restore(flags); |
| 175 | } |
| 176 | EXPORT_SYMBOL_GPL(rcu_irq_enter); |
| 177 | |
| 178 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
| 179 | |
| 180 | /* |
| 181 | * Test whether RCU thinks that the current CPU is idle. |
| 182 | */ |
| 183 | int rcu_is_cpu_idle(void) |
| 184 | { |
| 185 | return !rcu_dynticks_nesting; |
| 186 | } |
| 187 | EXPORT_SYMBOL(rcu_is_cpu_idle); |
| 188 | |
| 189 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ |
| 190 | |
| 191 | /* |
| 192 | * Test whether the current CPU was interrupted from idle. Nested |
| 193 | * interrupts don't count, we must be running at the first interrupt |
| 194 | * level. |
| 195 | */ |
| 196 | static int rcu_is_cpu_rrupt_from_idle(void) |
| 197 | { |
| 198 | return rcu_dynticks_nesting <= 1; |
| 199 | } |
| 200 | |
| 201 | /* |
| 202 | * Helper function for rcu_sched_qs() and rcu_bh_qs(). |
| 203 | * Also irqs are disabled to avoid confusion due to interrupt handlers |
| 204 | * invoking call_rcu(). |
| 205 | */ |
| 206 | static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) |
| 207 | { |
| 208 | reset_cpu_stall_ticks(rcp); |
| 209 | if (rcp->rcucblist != NULL && |
| 210 | rcp->donetail != rcp->curtail) { |
| 211 | rcp->donetail = rcp->curtail; |
| 212 | return 1; |
| 213 | } |
| 214 | |
| 215 | return 0; |
| 216 | } |
| 217 | |
| 218 | /* |
| 219 | * Record an rcu quiescent state. And an rcu_bh quiescent state while we |
| 220 | * are at it, given that any rcu quiescent state is also an rcu_bh |
| 221 | * quiescent state. Use "+" instead of "||" to defeat short circuiting. |
| 222 | */ |
| 223 | void rcu_sched_qs(int cpu) |
| 224 | { |
| 225 | unsigned long flags; |
| 226 | |
| 227 | local_irq_save(flags); |
| 228 | if (rcu_qsctr_help(&rcu_sched_ctrlblk) + |
| 229 | rcu_qsctr_help(&rcu_bh_ctrlblk)) |
| 230 | invoke_rcu_callbacks(); |
| 231 | local_irq_restore(flags); |
| 232 | } |
| 233 | |
| 234 | /* |
| 235 | * Record an rcu_bh quiescent state. |
| 236 | */ |
| 237 | void rcu_bh_qs(int cpu) |
| 238 | { |
| 239 | unsigned long flags; |
| 240 | |
| 241 | local_irq_save(flags); |
| 242 | if (rcu_qsctr_help(&rcu_bh_ctrlblk)) |
| 243 | invoke_rcu_callbacks(); |
| 244 | local_irq_restore(flags); |
| 245 | } |
| 246 | |
| 247 | /* |
| 248 | * Check to see if the scheduling-clock interrupt came from an extended |
| 249 | * quiescent state, and, if so, tell RCU about it. This function must |
| 250 | * be called from hardirq context. It is normally called from the |
| 251 | * scheduling-clock interrupt. |
| 252 | */ |
| 253 | void rcu_check_callbacks(int cpu, int user) |
| 254 | { |
| 255 | check_cpu_stalls(); |
| 256 | if (user || rcu_is_cpu_rrupt_from_idle()) |
| 257 | rcu_sched_qs(cpu); |
| 258 | else if (!in_softirq()) |
| 259 | rcu_bh_qs(cpu); |
| 260 | rcu_preempt_check_callbacks(); |
| 261 | } |
| 262 | |
| 263 | /* |
| 264 | * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure |
| 265 | * whose grace period has elapsed. |
| 266 | */ |
| 267 | static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) |
| 268 | { |
| 269 | char *rn = NULL; |
| 270 | struct rcu_head *next, *list; |
| 271 | unsigned long flags; |
| 272 | RCU_TRACE(int cb_count = 0); |
| 273 | |
| 274 | /* If no RCU callbacks ready to invoke, just return. */ |
| 275 | if (&rcp->rcucblist == rcp->donetail) { |
| 276 | RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1)); |
| 277 | RCU_TRACE(trace_rcu_batch_end(rcp->name, 0, |
| 278 | ACCESS_ONCE(rcp->rcucblist), |
| 279 | need_resched(), |
| 280 | is_idle_task(current), |
| 281 | rcu_is_callbacks_kthread())); |
| 282 | return; |
| 283 | } |
| 284 | |
| 285 | /* Move the ready-to-invoke callbacks to a local list. */ |
| 286 | local_irq_save(flags); |
| 287 | RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1)); |
| 288 | list = rcp->rcucblist; |
| 289 | rcp->rcucblist = *rcp->donetail; |
| 290 | *rcp->donetail = NULL; |
| 291 | if (rcp->curtail == rcp->donetail) |
| 292 | rcp->curtail = &rcp->rcucblist; |
| 293 | rcu_preempt_remove_callbacks(rcp); |
| 294 | rcp->donetail = &rcp->rcucblist; |
| 295 | local_irq_restore(flags); |
| 296 | |
| 297 | /* Invoke the callbacks on the local list. */ |
| 298 | RCU_TRACE(rn = rcp->name); |
| 299 | while (list) { |
| 300 | next = list->next; |
| 301 | prefetch(next); |
| 302 | debug_rcu_head_unqueue(list); |
| 303 | local_bh_disable(); |
| 304 | __rcu_reclaim(rn, list); |
| 305 | local_bh_enable(); |
| 306 | list = next; |
| 307 | RCU_TRACE(cb_count++); |
| 308 | } |
| 309 | RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count)); |
| 310 | RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(), |
| 311 | is_idle_task(current), |
| 312 | rcu_is_callbacks_kthread())); |
| 313 | } |
| 314 | |
| 315 | static void rcu_process_callbacks(struct softirq_action *unused) |
| 316 | { |
| 317 | __rcu_process_callbacks(&rcu_sched_ctrlblk); |
| 318 | __rcu_process_callbacks(&rcu_bh_ctrlblk); |
| 319 | rcu_preempt_process_callbacks(); |
| 320 | } |
| 321 | |
| 322 | /* |
| 323 | * Wait for a grace period to elapse. But it is illegal to invoke |
| 324 | * synchronize_sched() from within an RCU read-side critical section. |
| 325 | * Therefore, any legal call to synchronize_sched() is a quiescent |
| 326 | * state, and so on a UP system, synchronize_sched() need do nothing. |
| 327 | * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the |
| 328 | * benefits of doing might_sleep() to reduce latency.) |
| 329 | * |
| 330 | * Cool, huh? (Due to Josh Triplett.) |
| 331 | * |
| 332 | * But we want to make this a static inline later. The cond_resched() |
| 333 | * currently makes this problematic. |
| 334 | */ |
| 335 | void synchronize_sched(void) |
| 336 | { |
| 337 | rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && |
| 338 | !lock_is_held(&rcu_lock_map) && |
| 339 | !lock_is_held(&rcu_sched_lock_map), |
| 340 | "Illegal synchronize_sched() in RCU read-side critical section"); |
| 341 | cond_resched(); |
| 342 | } |
| 343 | EXPORT_SYMBOL_GPL(synchronize_sched); |
| 344 | |
| 345 | /* |
| 346 | * Helper function for call_rcu() and call_rcu_bh(). |
| 347 | */ |
| 348 | static void __call_rcu(struct rcu_head *head, |
| 349 | void (*func)(struct rcu_head *rcu), |
| 350 | struct rcu_ctrlblk *rcp) |
| 351 | { |
| 352 | unsigned long flags; |
| 353 | |
| 354 | debug_rcu_head_queue(head); |
| 355 | head->func = func; |
| 356 | head->next = NULL; |
| 357 | |
| 358 | local_irq_save(flags); |
| 359 | *rcp->curtail = head; |
| 360 | rcp->curtail = &head->next; |
| 361 | RCU_TRACE(rcp->qlen++); |
| 362 | local_irq_restore(flags); |
| 363 | } |
| 364 | |
| 365 | /* |
| 366 | * Post an RCU callback to be invoked after the end of an RCU-sched grace |
| 367 | * period. But since we have but one CPU, that would be after any |
| 368 | * quiescent state. |
| 369 | */ |
| 370 | void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
| 371 | { |
| 372 | __call_rcu(head, func, &rcu_sched_ctrlblk); |
| 373 | } |
| 374 | EXPORT_SYMBOL_GPL(call_rcu_sched); |
| 375 | |
| 376 | /* |
| 377 | * Post an RCU bottom-half callback to be invoked after any subsequent |
| 378 | * quiescent state. |
| 379 | */ |
| 380 | void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
| 381 | { |
| 382 | __call_rcu(head, func, &rcu_bh_ctrlblk); |
| 383 | } |
| 384 | EXPORT_SYMBOL_GPL(call_rcu_bh); |